Advertisement

Advertisement

BIG PHYSICS, BIG QUESTIONS –

Fruity formula could contain prostate cancer

By Gail Vines

A PROCESSED extract of orange peel may stop the spread of prostate cancer to other organs. Kenneth Pienta of the University of Michigan at Ann Arbor and colleagues at Wayne State University in Detroit have found that a chemically modified orange peel extract can slow the spread of malignant cells through the bodies of rats.

The research could ultimately lead to a pill that would prevent metastasis in prostate cancer – the migration of cancer cells from the primary tumour to other sites around the body. In many industrialised countries, prostate cancer is the most common form of cancer in men. It is often possible to treat the initial tumour in the prostate gland, but once the cancer spreads to other organs it is incurable. In the US alone, where screening for prostate cancer is widespread, more than 240 000 new cases are diagnosed each year. The annual US death toll from the disease is some 40 000.

Pienta and his colleagues took pectin, a carbohydrate found in orange peel and apple skin, and broke it down into smaller fragments by treating it first with alkali and then an acid. These fragments were soluble and so could be fed to rats in their drinking water.

The researchers first injected rats with prostate tumour cells, which would normally quickly spread to the animals’ lungs, resulting in about ten new tumours thirty days later. But the fragments seemed to stop the cancer cells in their tracks. Rats which drank a 1 per cent solution of the modified pectin fared much better than controls. Half of them developed no lung tumours at all, and the other half developed only two or three (Journal of the National Cancer Institute, vol 87, p 348).

Advertisement

Fragments of the modified pectin had previously been shown to dock with a molecule on the surface of tumour cells – a lectin known as galectin-3. Lectins are proteins that bind to carbohydrates and are thought to allow cells to recognise one another, which they must do before they can interact. Pienta and his colleagues speculate that the modified pectin stops galectin-3 binding to carbohydrates on the surface of other cells. As a result, the researchers believe, tumour cells can no longer stick to the walls of blood vessels and each other, and so cannot spread throughout the body and form secondary tumours.

Pienta and his colleagues are now trying to find out which pectin fragments bind to galectin-3, in the hope that these active ingredients can be made into a pill. Men who have just had surgery or radiotherapy for prostate cancer might benefit most, suggests one member of the research team, Harmesh Naik of Wayne State University.

A drug to prevent prostate cancer metastasis, is at least five years away, however. And other researchers warnm that the modified pectin might not work as well in human patients as in rats. “It would be wonderful if an orally active drug from a natural product could be found,” says Jonathan Waxman of Hammersmith Hospital in London. “But a panacea in rats does not necessarily translate into humans.” One encouraging sign, however, is that galectin-3 has been found on the surface of human prostate cancer cells. It is also possible that the modified pectin will prevent metastasis in other cancers.